MCNPX simulations of spallation experiments

Mitja Majerle

majerle@ujf.cas.cz

Outline

Phasotron and EPT experiment Simulations Disagreement between experiment

and simulation : Experimental uncertainties MCNPX code

Other applications of MC simulations

Dubna experiments

Phasotron Bare, lead target + 660 MeV protons Activation detectors longitudinally,

samples

Dubna experiments

EPT Complex setup, energies from 0.7-2.5

GeV Activation detectors, SSNTd, samples

Dubna experiments

+results from radial detectors, SSNTd, samples…

MCNPX simulations

PHASOTRON SETUP

EPT SETUP

•Geometry is implemented in MCNPX

•Incident particles are directed to the setup

•Neutrons are counted at the places of the detectors

Neutron spectra, cross-sections

•XS for convolution are calculated with the combination of TALYS and MCNPX codes

Comparison exp/simPhasotron experiment

Beam monitors Longitudinal detectors

Comparison exp/simEPT experiment

Activation detectors - radial

SSNTd

0

1

2

3

4

5

0 5 10 15

Radial distance [cm]

Bex

p/B

sim

Au-196Au-194Au-193Au-192Au-191

Energy range : 10-100 MeV Energy range : 200-1000 MeV

Comparison exp/simEPT - (n,) reactions

EPT has neutron reflector – polyethylene (most neutrons back to the system and induce (n,) reactions)

(n,) product Au-198 reliably tells us about the number of produced neutrons

Production rates of Au-198 are very well predicted by MCNPX

Comparison exp/sim Disagreement in the range 10-100

MeV Total number of neutrons is ok (n,) Activation detectors are NOT ok SSNTd are ok again

What are the possible reasons ? Experimental uncertainties Partially wrong code ?

Experimental uncertainties INFLUENCE OF THE SETUP PARTS

simplifications of the setup description different parts of the setup

SYSTEMATIC ERROR (not accurately known exp. conditions)

beam geometry reactions with protons inserted detectors

ACCURACY OF SIMULATION intra-nuclear cascade model used in calculations

PARAMETERS OF THE SETUP the number of produced neutrons (spallation,

fission, ..) k (criticality)

From the seminary in 2005 :

Polyethylene, Cd layer

The spectra were taken inside the 1st and 3rd gap.

No influence on HE neutrons.

1st gap, 3cm from axis

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

without Cd

without box

whole_setup

3rd gap, 3 cm from axis

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E-10 1E-08 1E-06 1E-04 1E-02 1E+00 1E+02 1E+04

without Cd

without box

whole_setup

absorption done by 238U resonance capture

Comparison of HE part of spectra

0,85

0,9

0,95

1

1,05

1,1

1,15

0,1 1 10 100 1000

Neutron energy [MeV]

Ratio

w ith Cd/all

w ith box/all

The wooden plate

Wooden plate under the target(1+2cm,0.5kg/l).

Without box. Detectors from top to

bottom. Asymmetry 5% =>

negligible wood influence. 0E+0

1E-5

2E-5

3E-5

4E-5

5E-5

-10 -5 0 5 10

Radial foil position [cm]

Pro

du

ctio

n r

ate

Au-198

Au-194

Aluminum and iron holders, upper iron plate

Two simulations with and without Al, Fe components. The results do not differ outside the limits of statistical error - (HE 3%, LE 10%)

The upper iron plate reduces the number of neutrons for 2%.

Beam profile

Simulations with 3mm, 3cm homogenous beams and with a beam with gaussian profile (FWMH=3cm).

Differences only for few percents.

Not important.-10

-8

-6

-4

-2

0

2

4

6

1 2 3 4 5 6 7 8 9 10

Foil and reaction number

beam

/3cm

-1 (i

n %

)

3mm/3cm-1

gauss/3cm-1

Beam displacement

Beam displaced for 3,5,8, and 10 mm.

Differences between results up to tens of % Displacement must be measured as accurately as possible !

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10

Foil and reaction

Dis

pla

ced

bea

m/c

ente

r b

eam

-1 (

in %

)

3 mm

5 mm

8 mm

10 mm

The influence of detectors on neutron field

Metal plate on top reduces the number of neutrons only for 2%. Our detectors are much smaller.

Golden strap (2mm, 4mm) in the first gap has no influence on detectors in other gaps.

Only 0.1 mm thick golden strap is an obstacle for thermal neutrons : it can reduce the production rates of reactions with thermal neutrons inside the same gap for 20%.

Intra-Nuclear Cascade models

In MCNPX are 3 models (above 150 MeV): Bertini CEM Isabel

The differences are up to 30% (standard, our detectors).

-25

-20

-15

-10

-5

0

5

10

15

20

25

30

1 2 3 4 5 6 7 8 9 10

Foil and reaction

mo

del

/ber

tin

i-1

(in

%)

cem

isabel

-40

-30

-20

-10

0

10

20

30

40

50

60

1 6

11

16

21

26

31

36

41

46

51

56

61

Foils and reactions of the Rez group

mo

del

/BE

RT

INI-

1 (i

n %

)

CEM/BERTINI-1

ISABEL/BERTINI-1

Total uncertainty:50%

Setup description < 10%Experimental uncert. ca 20%Differences in models ca 30%

Total for SSNTd :>>50%

Comparison exp/simPhasotron experiment

Beam monitors Longitudinal detectors

Comparison exp/simEPT experiment

Activation detectors - radial

SSNTd

0

1

2

3

4

5

0 5 10 15

Radial distance [cm]

Bex

p/B

sim

Au-196Au-194Au-193Au-192Au-191

Energy range : 10-100 MeV Energy range : 200-1000 MeV

Systematical error in analysis ?

HPGe detectors simulations (efficiencies, cascade coefficients)

Good knowledge of processes Consistent results Little chance to explain the

discrepancies…

Is MCNPX wrong ?

Calculations with simplified setup were repeated in FLUKA code (Maxime Oden)

The same, wrong trends exp/sim were obtained (presented on Prague Physics summer school)

Is MCNPX wrong ?Spallation experiments on thin targets

Recent experiments with protons directed on thin targets Leroy, Ledoux Trebukhovskiy, Yurevich Meigo…

Some of their simulations show that there are exp/sim discrepancies in the region 20-80 MeV

.. or is something wrong with our experiments ?

Repeat one experiment, which we believe that is good and see if we get the same results

Perform experiments with changed setup (without blanket, uranium)

.. not very likely, so ..

Other work connected to ADS simulations

Polish subcritical setup, based on MARIA reactor (Gael de Cargouet)

Beam from horizontal channel of the reactor

EK-10 rods

Blanket made of ENH, BaF rods and lead

GAMMA-MD

Pb target Graphite

block

2.33 GeV deuterons

Neutron spectrum in detectors

1E-8

1E-7

1E-6

1E-5

1E-4

1E-3

1E-2

1E-1

1E+0

1E-9 1E-7 1E-5 1E-3 1E-1 1E+1 1E+3

Neutron energy

Neu

tro

n f

lux

[p-1

cm

-2]

50 cm from target20 cm from target

Simulations unify experimental data from different experiment well, but they are not precise everywhere

Maybe we can confirm exp/sim discrepancies from completely different experiments

That many simulations require a lot of processor power (CESNET)

Thank you for your attention.

Conclusion